In the prior art, a pre-stressed insulated tubing includes an inner tube, an outer tube and an insulating system formed between the inner tube and the outer tube. The following measures are usually used to form the insulating system: first, an outer wall of the inner tube and an inner wall of the outer tube are sandblasted so as to make surfaces of the tube walls smooth, thereby facilitating vacuum pumping; then, the outer wall of the inner tube is wound around with a plurality of layers (usually six layers) of thermal insulation materials or heat preservation materials such as glass wool cloth, aluminium silicate wool, aluminum foil, etc., getter is added into a cavity formed between the inner tube and the outer tube, and normal vacuum pumping is performed to achieve effects of thermal insulation and heat preservation. In the prior art, apparent heat-conduction coefficient of the pre-stressed insulated tubing is usually larger than 0.003 w/m° C., insulating level is D, and vacuum degree is equal to or less than 5 Pa.
With the development of the petroleum extraction technology, heavy oil extraction technologies such as steam huff and puff, steam drive and SAGD (Steam Assisted Gravity Drainage) have been widely used, and they heat oil layers by using steam of high temperature and high degree of dryness, maintain the oil layers at certain pressure, and drive crude oil to producing wells surrounded to be extracted out, so as to make the oil driving efficiency increase progressively and enhance the oil recovery. However, the steam of high temperature and high degree of dryness in the oil extraction technology of steam huff and puff, steam drive and SAGD sets even higher demand on the insulating performance and working life of the pre-stressed insulated tubing. When the existing pre-stressed insulated tubing is used in steam huff and puff, steam drive and SAGD to continuously inject steam by a corresponding steam injection well, since the inner tube and the outer tube of the steam injection well are usually made of carbon steel materials, when they are used under an oil extraction environment of high temperature and high pressure for a long time, hydrogen ions in carbon steel easily drift out to penetrate into the cavity between the inner tube and the outer tube to form hydrogen, which decreases the vacuum degree in the cavity, thereby destroying the insulating system of the pre-stressed insulated tubing and decreasing the insulating performance of the pre-stressed insulated tubing. In addition, since the outer wall of the inner tube of the traditional pre-stressed insulated tubing is wound around with a plurality of layers of glass wool cloth, aluminium silicate wool, aluminum foil etc., the inner and surfaces of these thermal insulation materials or heat preservation materials absorb a large amount of gas, and the gas will release under the traditional vacuum pumping and “contaminate” the vacuum so that a part of harmful gas will remain in the body of the tubing; when the pre-stressed insulated tubing is under high temperature for a long time, the harmful gas will easily destroy the vacuum insulating system, which will shorten the working life of the pre-stressed insulated tubing (the working life of the existing pre-stressed insulated tubing is merely about 2 years) and affect normal production of oil wells.
At the same time, in the process of manufacturing the pre-stressed insulated tubing since workers are required to wind around the outer wall of the inner tube with thermal insulation materials such as glass wool cloth, aluminium silicate wool, aluminum foil etc., not only the labor intensity is large, but also microfiber released from the materials such as glass wool cloth, aluminium silicate wool, aluminum foil and etc. will bring harm to health of human bodies; it is inevitable for human bodies to encounter dust and noise contamination when the inner tube and the outer tube of the pre-stressed insulated tubing are sandblasted.